The present invention relates to a polyamide filament comprising a specific polyamide resin composition. More particularly, the present invention relates to a polyamide filament which exhibits high heat shrinkage in boiling water and which can be made into a fabric with excellent look and feel. The present invention also relates to a process for producing a polyamide filament exhibiting high heat shrinkage in boiling water comprising melt-spinning a specific polyamide composition and cold stretching the spun filamentous material.
Polyamide filaments which are generally called nylon fibers are easy to dye and have excellent wear-resistance, so that they are widely used for stockings, carpets, etc. However, polyamides which are conventionally used for fabrics are mainly nylon 6 and nylon 66, and the nylon 6/66 copolymer is used only in special cases. The heat-shrinkage in boiling water of any of these nylons is 10 to 15%, so that there is a limited range of applications for such products. It is considered that if it is possible to produce a polyamide fiber exhibiting high heat-shrinkage in boiling water, a new application can be developed in the filed of clothing and the like by, for example, using fibers having different shrinkage for the warp and the weft so as to produce a fiber exhibiting a bulky look and feel.
As one of these methods, Japanese Patent Application Laid-Open (KOKAI) No. 52-85516 (1977) discloses a high heat shrinkable polyamide fiber produced by stretching a filament of a terpolymerized polyamide consisting essentially of hexamethyleneadipamide, hexamethyleneterephthalamide and hexamethyleneisophthalamide and having a glass transition temperature of not lower than 80.degree. C., at a stretching temperature higher than the vicinity of the glass transition temperature. However, the terpolymerized polyamide requires special manufacturing conditions in order to be made into fibers because it is whitened or can not be stretched by cold stretching which is used for ordinary nylon 6, in other words, stretching without any special heating.
Compositions of an aromatic polyamide resin and an aliphatic polyamide resin are shown in Japanese Patent Application Laid-Open (KOKAI) Nos. 58-38751 (1983) and 62-41261 (1987). Although Japanese Patent Application Laid-Open (KOKAI) No. 58-38751 (1983) discloses a composition consisting essentially of an aliphatic polyamide resin, an aromatic polyamide resin and a toughness improving agent, this composition is mainly used in the field of injection molding and only applications of a molded product are shown.
Although Japanese Patent Application Laid-Open (KOKAI) No. 62-41261 (1987) also discloses a composition consisting essentially of an aliphatic polyamide resin. The only use described for this composition is as a biaxially-oriented shrinkable film. Since manufacturing methods and conditions are greatly different between a biaxially-oriented shrinkable film and a filament produced by cold-stretching, one cannot predict with any degree of certainty the shrinkage properties of a filament from the shrinkage properties of a film.
As a result of the present inventors' studies, it has been found that by using a composition of an ordinary aliphatic polyamide resin such as nylon 6 and nylon 66 and a specific aromatic polyamide resin, one can obtain a polyamide filament which may be produced by cold-stretching and which has a high heat-shrinkage in boiling water. The present invention has been achieved on the basis of this finding.